Synovial joints (diarthroses, diarthroidal joints) are the most common joints in the human body providing the greatest range of motion. Synovial joints include a capsule surrounding the articulating bone surfaces. The capsule is formed with a synovial membrane that excretes synovial fluid into the joint space and hyaline cartilage that lines the articulating ends of the joint bones and lies within the fluid-filled capsule.
One of the most frequent causes of physical disability among adults is osteoarthritis, which affects the articular cartilage as well as adjacent tissues of synovial joints. Damage to the articular cartilage due to traumatic injury, disease, or the natural aging process can lead to osteoarthritis. Symptoms of mild osteoarthritis can include joint pain, stiffness, and loss of mobility, while severe cases can include gross joint deformity and bony overgrowth, complete cartilage loss and collapse of the underlying subchondral bone.
Cartilage is an avascular tissue including between about 5 and 10% by weight chondrocytes. Chondrocytes have limited mobility as well as limited ability to divide and regenerate damaged tissue. Thus, damage to the articular cartilage is not accessed by blood, macrophages, or mesenchymal stem cells, and exhibits poor healing. Osteochondral damage that extends through the full thickness of the cartilage and encompasses damage to the subchondral bone will be accessed by blood and mesenchymal stem cells, but this in turn can lead to neovascularization and ingrowth of fibrocartilage to the cartilage layer, rather than regrowth of healthy cartilage. Moreover, osteochondral defects can often lead to an ingrowth of osteocytes in the cartilage area, followed by calcium deposition and new bone growth, leading to further deformation of the joint.
Attempts have been made to develop treatment methods that can address the unique requirements of the two different, adjacent tissue types so as to encourage proper healing of both the articular cartilage and, where necessary, the subchondral bone. For instance, U.S. Pat. No. 6,626,950 to Brown, et al. discloses a prosthetic implant including an anchoring post embedded within a tissue scaffold, the tissue scaffold including a porous ceramic phase, a porous polymer phase, and an interphase between the two. U.S. Pat. No. 7,361,195 to Schwartz, et al. discloses an orthopedic device including a plug to be positioned in hole formed in damaged cartilage and an anchor configured to support the plug. U.S. Pat. No. 6,454,811 to Sherwood, et al. discloses devices for tissue engineering that have a gradient of materials, macroarchitecture, microarchitecture, or mechanical properties that can be used to select or promote attachment of specific cell types prior to or following implantation.
While the above describe advances in the art, room for improvements exists. For instance, what is needed in the art are osteochondral implants that can encourage the growth and development of two different tissue types immediately adjacent to one another while being securely held in place in an osteochondral defect. What are also needed in the art are implants that can encourage adequate flow of nutrients to and waste from cells throughout a developing tissue culture, and thus avoid necrosis at the center of the developing tissue culture.